Losing Oil Pres and Revs

[ReodDai]

Having a problem with oil pressure and revs dropping sometimes after the car as been driven decently hard. Like after my 15.682 run the car almost died coming back. Yesterday after taking 98v6 for a ride the rpms dropped to like 300 and the oil pressure dropped to like 20(It normally sits around 60) just for an instant then came back up. It only does this when I push the clutch in to change gears and normally only when its been driven hard. Also sometimes I can visibly see the lights on my car dim at the same time. If the revs and pressure drop tho I can hear the car stumble for a sec.

Any ideas? Just want to make sure its not something serious.

[terminaldegree]

Well I think I can answer for two of your issues...

The oil pressure will drop down below its normal number at idle when the motor is turning below idle speed, sometimes pretty significantly. Say if you let the clutch out too quickly in 1st gear without giving enough gas [almost stalling the car], I notice the oil pressure drop sharply for a fraction of a second. I think the minimum specification I've seen is 60psi @ 1850rpm, and it doesn't mention a number at idle. Also realize that once the oil gets hot, the pressure gauge will read lower at idle than when the motor is cold. For my car it's a difference of 5-10 psi at idle depending on how hard I'm driving it. The only other thing I wonder is if your oil is newish or has a few thousand miles on it, as I've heard oil viscosity breaks down with mileage and may result in the oil being a little too thin when hot, decreasing the pressure reading.

The lights dimming is simply the inability of your alternator to do its job properly at such a low engine speed. At normal idle rpm, the alt can barely keep up with basic electrical demands. Subtract 100-200 rpm, and it can't do its job at all. I think you need to be up around 2000rpm before it really is able to operate at the peak charging rate.

The engine idle speed thing I can't answer. Take everything I say with a grain of salt, as I'm not a mechanic. You have both a '98 and an '00? Jealousy...

[ July 14, 2004, 02:15 AM: Message edited by: terminaldegree ]

[ReodDai]

No 98v6 is a member of this board lol.
Kinda sad that my alternator can't keep up with my car. Only thing that was on was the headlights, interior lights and the motor.

[terminaldegree]

I just edited that post a couple of minutes ago. Looks like we're playing tag.

Drop me a line next time you're headed to Austin. I'll be living in San Marcos starting this August.

[ReodDai]

I'll be in austin from August 10th through somewhere in the 20s. For my summer break lol Thats all I get.

[Pastor Larry Roques]

Having just dealt with an alternator issue on another car, I have just a little better understanding of the way newer cars operate. The EFI system on your car depends upon the alternator to keep the juice flowing to all of the systems....no Electronic Fuel Injection...no running engine. If the engine RPMs for whatever reason...oil viscosity...what have you...reduces...it will cause a kind of chain reaction that will cause the car to be starved for fuel...oxygen...and just about everything else it takes to keep it running. I learned these things on the side of the road on a cell phone. [img]graemlins/rofl.gif[/img]

[94TeaL]

what kinda oil you run weight too?

[ReodDai]

10w-30

[94TeaL]

Originally posted by ReodDai:
10w-30

Well in the summer months people who run 5w30 should switch to 10w30 due to this, Too hot and 5w30 thins out..

[ReodDai]

Apparently not, its summer and I'm running 10w30 and still have the problem lol.

[Ian]

seriously, check your battery cables. loose ground during shifts could do it.